To manufacture aircraft components, such as stringers, composite material is often applied to forming bladders and then wrapped with an impermeable membrane, such as a vacuum bag, before being cured. During cure, vacuum is applied via a vacuum port in the vacuum bag, causing the vacuum bag to deflate against the composite material and causing the bladder to inflate, pressing the composite material between the vacuum bag and the bladder.
Forming bladders are susceptible to developing leaks, especially when exposed to high temperatures and pressures in autoclaves during cure. Some leaks are detected after a cure cycle that were not apparent prior to the cure. The added pressure and heat during cure may cause undetected leaks in the bladder to develop into larger, detrimental leaks during the autoclave cure cycle. It is also possible that human error may create leaks in bladders at a stage in which the bladders cannot be removed from the composite material or repaired. Methods have been developed for detecting vacuum bag leaks, though the methods are not effective at locating precise locations of these leaks. These prior art methods also fail to detect bladder leaks during cure cycle. Furthermore, prevention of resulting damage from such leaks is difficult to manage.
One prior art method of detecting leaks in a vacuum bag includes placing a vacuum gage in line with a vacuum source, between the vacuum bag and the vacuum source, to sense vacuum decay. If a leak occurs in the vacuum bag or in the bladder prior to reaching a critical stage cure temperature, the cure cycle may be aborted and the leak in the vacuum bag may be fixed. For example, the operator may open a door of the autoclave and search for the leak using an ultrasonic microphone. Once the leak is located, the operator may fix the leak by various patching and repair methods known in the art. However, it is unknown what effect a leaking bladder has on overall vacuum bag integrity. Some of the vacuum decay detected by the vacuum gage could be attributed to a leaking bladder. In this case, the operator might detect vacuum decay and suspect that there is a vacuum bag leak. The operator would then abort the cure and search for a vacuum bag leak without finding one. If the leak is really merely a pin hole in the side of the bladder, the operator can't access or fix this bladder leak, since he doesn't know whether the vacuum bag or the bladder is leaking.